Gold’s great virtues of malleability, ductility, reflectivity, resistance to corrosion and unparalleled ability as a thermal and electrical conductor mean it is used in a wide variety of industrial applications consuming close to 300 tonnes annually.
Gold (Au, from Latin “Aurum” (World Book Dictionary) is the most non-reactive of all metals — it is benign in all natural and industrial environments. Gold never reacts with oxygen (one of the most active elements), which means it will not rust or tarnish. Gold is among the most electrically conductive of all metals. Since electricity is basically the flow of charged particles in a current, metals that are conductive allow this current to flow unimpeded. “Gold is able to convey even a tiny electrical current in temperatures varying from -55. to +200. centigrade.” (Gold Institute) Gold is the most ductile of all metals, allowing it to be drawn out into tiny wires or threads without breaking. Consequently, a single ounce of gold can be drawn into a wire five miles long. Gold’s malleability is also unparalleled. It can be shaped or extended into extraordinarily thin sheets. For example, one ounce of gold can be hammered into a 100 square foot sheet.
Gold is the most reflective and least absorptive material of infrared (or heat) energy. High purity gold reflects up to 99% of infrared rays. Gold is also an excellent conductor of thermal energy or heat. Since many electronic processes create heat, gold is necessary to transfer heat away from delicate instruments. Gold alloy is the most tenacious and long-performing material available for protection of these temperatures.
Geologists use the latest technology such as satellite surveys and geochemistry to locate an ore deposit. Computers are used to design the mine, which requires precise and accurate measurement of the ore deposit. Construction begins following the lengthy process of receiving permits. As holes are drilled for blasting, samples of ore are examined to determine grade and metallurgical characteristics. The broken rock is marked by type for efficient processing. Based on its metallurgical makeup, a dispatcher directs truck operators to deliver the ore to the correct processing location.
Low-grade ore is roughly broken into small chunks and placed on carefully lined pads where a dilute cyanide solution is distributed over the surface of the heap. The solution percolates through the heap and the cyanide dissolves the gold. This solution containing dissolved gold is then collected. Refractory ore containing carbon is roasted to over 1,000 degrees Fahrenheit, burning off the sulfide and carbon. The product of this process is an oxide ore, which is routed to the leaching circuit. Oxide ore is sent directly to the leaching circuit where cyanide dissolves the gold. Sulfide refractory ore without carbon is oxidized in an autoclave to liberate the gold from sulfide minerals, then it is sent to the leaching circuit. Treated, high-grade ore is leached with cyanide.
The gold is absorbed out of solution onto activated carbon. The remaining cyanide solution is recycled. The gold loaded carbon is moved into a vessel where the gold is chemically stripped from the carbon, which is then recycled. Gold is precipitated from the solution electrolytically or by chemical substitution. The pure gold is then melted into dore’ bars containing up to 90 % gold. Dore’ bars are then sent to an external refinery to be refined to bars of 999.9 parts per thousand pure gold.
The prime use is in electronics. Our age of high technology finds it indispensable in everything from pocket calculators to computers, washing machines to television and missiles to spacecraft. The rocket engines of American space shuttles are lined with 35% gold brazing alloys to reflect the 3300. heat, and the lunar modules of the Apollo program that put men on the moon were shrouded with gold foil acting as a radiation shield. (World Gold Council) More commonly, the humble touch telephone in your home typically contains 33 gold-plated contacts. The plating of such contacts in switches, relays and connectors is the major application of gold in electronics. Contacts are electroplated with a very thin film of gold using gold potassium cyanide (GPC), often called plating salts. This touch of gold on a contact ensures rapid dissipation of heat and guarantees freedom from oxidation or tarnishing at extreme low or high temperature, thus providing an atomically clean metal surface with an electrical contact resistance close to zero. Not surprisingly “nothing is as good as gold” to provide total reliability, whether out in space or in the home. The production of plating salts accounts for 70% of the more than 150 tonnes of gold used annually in electronics. Although new technology has enabled plating thickness to be pared down to less than one-thousandth of a millimeter of gold, gold consumption has been maintained because of the myriad new electronic applications.
Gold’s other main role in electronics is in semi-conductor devices, where fine gold wire or strip is used to connect parts such as transistors and integrated circuits, and in printed circuit boards to link components. Again, the need for reliable connections makes gold indispensable. This bonding wire is one of the most specialized uses of gold; it is highly refined to 999.99 purity and the wire has a typical diameter of one-hundredth of a millimeter. Japan is the major fabricator of electronics products in the western
world, accounting for over 45% of gold consumption, followed by the United States with nearly 30%. The United Kingdom and Germany are the only other significant contributors at about 6 and 7% respectively, although South Korea is growing. Dental gold is the second important sector. Gold has been used in dentistry for almost 3000 years. The Etruscans in the 7th century BC used gold wire to fix substitute teeth when their own were lost. In the 16th century an early dental text book recommended gold leaf for filling cavities.
Gold’s malleability and resistance to corrosion render it eminently suitable for dental use, although its softness means that it must be alloyed to retard wear. The most common companion metals are platinum, silver and copper. A typical alloy may contain anywhere from 620 – 900 fine gold depending on the precise end-use. In recent years the price of gold has resulted in a trend towards cheaper alloys with as little as 30% gold and towards palladium-based alloys which contain scarcely 2% gold.
Gold alloys have also suffered competition from new techniques, such as ceramic dental crowns. In addition, social security payments for gold dental work have come under tighter scrutiny; reductions in such insurance payments make gold use more price sensitive. These factors initially contributed to a sharp fall in gold use by the dental sector, from 64 tonnes in 1980 to 48 tonnes by 1987. However, there has since been a recovery because of its non-allergic properties; demand has revived to 60 tonnes annually. Japan is the leading dental gold fabricator, accounting for roughly 28% of the market, followed by Germany and the United States. There is Significant unrecorded use, however, in Asia and Latin America where it is not unknown for dentists to melt down gold coin to make their own alloy.
Other applications for gold include decorative plating of costume jewelry, watchcases, pens and pencils, spectacle frames and bathroom fittings. Gold-based points are used for decoration of china and glass. Demand for gold from this sector is around 90 tonnes per year. The gold is used in various forms, such as rolled gold and gold fill, although both of these are under competition from new techniques. On the other hand, the use of gold electroplating in watchcases and similar products is increasing. Visually, the most spectacular use of decorative gold is gold leaf which has been used for centuries to adorn the domes or ceilings of public buildings, because its resistance to corrosion means it will outlast paint by many years. Gold’s ability to reflect heat in summer and help retain it in winter has also led to the use of glass coated with a thin film of gold in several modern buildings, especially in North America; one ounce of gold covers typically one thousand square feet of glass. This reflective glass can cut cooling and heating costs by 40%. The major consumption of decorative gold is in the United States and Japan. All told, the industrial uses of gold provide a very steady element in gold demand, requiring more than the equivalent of all Australian gold production annually. In the last 6,000 years over 125,000 tonnes of gold has been recovered, first from alluvial deposits in rivers and then by mining. But most of it has been produced in the last 150 years, since the major discoveries in the United States and Australia in the mid-19th century. Then, in the short span of 50 years, more was mined than in the preceding 6,000.
Today, worldwide production amounts to about 2,300 tonnes annually, having doubled since 1980 due to higher prices and new technology. Although gold is mined in almost sixty countries, the following are the major producers.
George Harrison discovered gold on Langlaagte farm near Johannesburg in February 1886. Soon, South Africa was the world’s premier producer, a position that it has held almost continuously ever since. In just over a century, more than 45,000 tonnes of gold have been mined in South Africa, about 40% of all gold ever produced. The gold was found in an arc of “reefs” stretching from 40 miles east of Johannesburg to 90 miles west, then swinging down to the Orange Free State 200 miles south-west. The reefs vary in thickness, and slope in towards the centre of the arc to depths of at least 5,000 metres. Since gold is buried deep underground, new mines are expensive and take over five years to bring into production.
The peak year for production was 1970 when output topped 1,000 tonnes. Since then it has fallen to around 550 tonnes (under 25% of world output), but South Africa is likely to remain the foremost producer into the next century.
The California gold rush began in January 1848 after the discovery of gold in the tailrace of Sutter’s Mill in Sacramento Valley. Almost half a million prospectors swarmed to California, helping to open up the American west. But output peaked temporarily in 1853. Thereafter production waned and, apart from a brief resurgence in the 1930s, declined to 30.5 tonnes by 1980, when the high gold price, coupled with new production techniques, revived the industry. By 1995 output reached 329 tonnes, 60% from the state of Nevada. The richest deposit is the Carlin Trend with over 30 open-pit operations, of which the largest is Gold strike with an expected average production of over 50 tonnes per year.
Historically, Russia was one of the earliest sources of gold. Alexander the Great conquered Armenia in 33 BC in order to obtain its gold, but a discovery in the Urals in 1774 triggered the modern industry. By the 1840s Russia was the leading producer, until eclipsed by the California gold rush. After the Revolution, Stalin encouraged mining and the Soviet Union was the second biggest supplier until overtaken by the United States in 1991. Overall Soviet production peaked at 285 tonnes in 1989, before falling to about 250 tonnes in 1991, of which some 150 tonnes was from Russia itself. Important new mines are being developed in Kazakhstan and Uzbekistan.
Gold was first discovered in Australia in 1851 near Bathurst, New South Wales, transforming it from a mere penal colony. Output peaked in 1865 at 95 tonnes, but fortunes revived with discoveries at Kalgoorlie, Western Australia, in 1893. The second rush, focusing on the diggings along Kalgoorlie’s famous “Golden Mile”, lasted a decade. By 1903 output had risen to 199 tonnes, a level not surpassed until 1988. The gold boom of the 1980s changed everything. The revival focused on Kalgoorlie. The “Golden Mile” is being worked as one immense crater whose yearly output is close to 20 tonnes. Australian output in 1995 was 254 tonnes of which 75% came from Western Australia.
Canada only became a serious producer with the discovery of gold in the Klondike tributary of the Yukon River in 1896. 75 tonnes of alluvial gold was recovered in the first three years. The future of the industry, however, lay underground in the Pre-Cambrian shield that blankets Northern Ontario and Quebec, which provides over 80% of Canada’s gold output.
The first mine, Dome, opened in 1909 and is still operating. The price rise to $35 in 1934, stimulated production to 172 tonnes in 1941. Thereafter mining declined; by 1978 only 50 tonnes was produced. The industry revived in the 1980s with the discovery of the Hemlo deposit in northern Ontario.
Three mines are operating at Hemlo and producing 35 tonnes annually, with the Williams mine alone accounting for 15.5 tonnes. Hemlo helped output to a record 175 tonnes in 1991, but it has since declined. The only major new deposit is Eskay Creek in British Columbia.
Gold was recovered from alluvial deposits in the Andes as early as 1000 BC. However, significant production did not begin until the 18th century with discoveries in Brazil. The Mineracao Morro Velho mine in Minas Gerais opened in 1835 and is the world’s oldest continually worked mine.
Brazil’s output soared in the 1980s from alluvial deposits in the Amazon basin; the richest was Serra Pelada, hill of gold, from which 13 tonnes was excavated by thousands of garimpeiros (prospectors) in a single year. Total production has stabilized at around 75 tonnes annually, of which half comes from formal mines, the rest from garimpeiros at alluvial deposits. The rest of Latin America is the focus of much exploration and investment by North American and South African mining companies, which has pushed overall annual output towards 280 tonnes.
Chile has low-grade deposits high in the Andes, including El Indio and La Coipa. Bolivia has a new mine at Kori Kollo; Guyana has developed the Omai open pit ; Peru has new mines at Yanacocha and Maqui Maqui; in Venezuela La Camorra mine opened in 1994 and a major resource at Las Cristinas has been identified; Uruguay has opened the Mahoma mine and Argentina may develop the Majo de la Alumbrera deposit.
Gold has been mined in China for over 1,000 years, mainly in Shandong province. A major investment programme has lifted official production close to 100 tonnes annually in the 1990s, but local cooperatives and unofficial alluvial mining probably contribute another 30-40 tonnes. All formal mine output is sold to the People’s Bank of China, which re-sells some gold for local jewelry manufacturers. International mining companies are providing expertise and anticipate getting into joint venture projects.
Ghana has been renowned as the gold coast for 2,000 years. In the 1990s its mining industry is undergoing a major revival which has quadrupled output to over 50 tonnes annually. The Ashanti mine, which celebrates its centenary in 1997, contributes much of the output, but there are new joint ventures with foreign mining groups.
Indonesia and Papua New Guinea, which have many epithermal gold deposits, have become significant producers in the 1990s. The opening of the Misima Island and Porgera mines has pushed Papua New Guinea’s output to about 60 tonnes annually. Another large low-grade mine, Lihir Island, is due in the late 1990s. Indonesia is producing annually over 70 tonnes in the mid-90’s, ten times more than a decade ago.
Gold can be called the most useful material on earth, next to duct tape, and has and always will be extremely important to man. This will prove especially true in the information and space age. Its ductility, malleability, reflectivity, resistance to corrosion and unparalleled ability as a thermal and electrical conductor will insure that it remains as important as it is today.
Gold Institute,1996, http://www.goldinstitute.com/facts.html
World Book Dictionary, Volume one, 1990, pg. 133
World Gold Council, http://www.gold.org/pages/indu1.html